The background of this invention is fairly represented by U.S. Pat. Nos. 3,000,237, 3,063,349, 3,108,327 and 3,112,164, wherein various methods are disclosed for forming molds for use in making duplicate steel rule dies adapted to be grouped for gang-forming of cardboard blanks by means of reciprocating, flatbed-type press apparatus.
Although such dies formed by the methods disclosed in the before mentioned patents and by other methods have been used successfully for many years to form foldable carton blanks, a particular difficulty resides in the fact that the individual dies do not exactly repeat the design pattern for the rules of the die, even though the individual dies are all made from a common mold, with the result that the blanks cut from an assembly of these dies in a gang-forming operation may vary in critical dimensions. A particular reason for this is that the basic mold itself becomes worn from the placement of the successive set of rules to be cast into the rigid base of the working die. Thus, because of the lack of repeat accuracy in the prior die making methods, it has been the practice to number or otherwise identify the blanks formed from the individual dies comprising an assembly thereof and to keep the carton blanks so formed separate so that production can be allocated to specified automatic carton filling machines properly and individually adjusted to receive the same. The filling machines operate with such close tolerance that very often they cannot use the mixed blanks from multiple die blanking operations. A similar problem often arises with the automatic folding and glueing equipment which is designed to take cartons of particular dimensions.
These and other difficulties in the prior procedures for making duplicate steel rule dies have confined the use of such dies to flat-bed reciprocating presses and the more economical, high speed production of the rotary press type of apparatus has, in the main, been unavailable to the steel rule die cutting art. A particular reason for this is the very high cost of constructing a rotary blanking die by conventional methods and the inability, heretofore, of molding duplicate curved dies for a gang-forming operation by rotary press means.
Thus the instant invention has as its main objective a method of forming duplicate dies designed for high speed rotary press operation which also overcomes the before mentioned problems and assures that each die in an assembly thereof will be exactly like all of the others in all critical dimensions.
Although the present invention is concerned principally with producing dies for rotary presses, the method in its broadest aspects is not limited to dies for rotary presses.